noested.closures.refactor.js

const movieLists = [
  // ...
];

const boxartSizeRestrictions = boxart =>
  boxart.width === 150 && boxart.height === 200;

const videoBoxartMapper = (boxart, video) => ({
  id: video.id,
  title: video.title,
  boxart: boxart.url
});

const videosIterator = video =>
  video.boxarts
    .filter(boxartSizeRestrictions)
    .map(boxart => videoBoxartMapper(boxart, video));

const movieListIterator = movieList => movieList.videos.flatMap(videosIterator);

const result = movieLists.flatMap(movieListIterator);
console.log(result);